SEALANT APPLICATION
THE TWO CRITERIA UNDERLYING A GOOD APPLICATION
Introduction
For a sealant application to be successful, you must give the joint a convex shape and make it sufficiently wide.
Joint shape
With the exception of some sealants which harden following a chemical reaction, all sealants contain solvents or water; evaporation is therefore the process through which they dry. These products must be given a convex (domed, curved out) shape when applied. The convex shape allows stress-free evaporation as the joint dries. On the other hand, a concave or flat shape builds a tension in the sealant since the joint surface lengthens as the joint dries. The sealant reacts like a rubber band, i.e. the tension increases as it is being pulled.
Even if it is preferable to give them a convex shape, silicone- or
polyurethane-based chemical can be applied with a flat shape.
Joint width
The width of a joint depends on the surfaces involved. If you apply a
joint on fresh surfaces, you must take into account how the material
moves and the product’s elasticity. If the surface was already covered
with sealant, the new joint must be a little larger than the joint it
will replace. The joint must be large enough (at least 6 mm x 6 mm or ¼
in. x ¼ in.) and cover at least 3 mm (1/8 in.) over each of the surfaces
to be joined. Widths must be increased in the following cases:
• if defects must be hidden, for instance improperly cut clapboards;
• if the gap between materials is wider than 3 mm (1/8 in.).
Minimum joint width
Checklist
Method
Applying a sealant:
Cut the cartridge nozzle at a 90º angle, making it a little thinner than
the required joint width. This 90º angle makes it possible to lay a
convex joint.
2. Pierce the thin aluminum membrane which isolates the cartridge content
from the nozzle. Cleanly break the membrane; if the hole is too small,
it may prove difficult to extract the sealant.
3. Insert the cartridge in a caulking gun.
4. Lay down the sealant on the surface intersection while pressing the
caulking gun’s handle and moving the gun along without stopping. The
cartridge’s nozzle must not go back over freshly applied sealant.
5. Keep the pressure even. If the pressure is too heavy, irregularities
form in the joint’s shape. If too light, the sealant is laid on the
surface without proper adhesion.
6. Make the joint large enough (6 mm x 6 mm or ¼ in. x ¼ in.) and cover
each of the surfaces to be sealed with at least 3 mm (1/8 in.) of
sealant.
